imx8mp-phyboard-pollux-rdk: sync with kernel devicetree from v6.8-rc2

sync devicetree with kernel v6.8-rc2.

New commits on kernel v6.8-rc2:
4a58fcdb1818 arm64: dts: imx8mp-phyboard-pollux: Add support for RS232/RS485
3bd7fdcc359e arm64: dts: imx8mp-phyboard-pollux: Add gpio-line-names
f5faa633daf8 arm64: dts: imx8mp-phyboard-pollux: Enable USB support
27c0dc128d04 arm64: dts: imx8mp-phyboard-pollux: Add flexcan support
fa2a1ec50456 arm64: dts: imx8mp-phyboard-pollux: Add missing usdhc clocks assignment
055e38c76388 arm64: dts: imx8mp-phyboard-pollux-rdk: Fix led sub-node names

Signed-off-by: Benjamin Hahn <B.Hahn@phytec.de>